This invention relates to an electronic musical instrument wherein, by merely depressing one key, a renditional effect such that the pitch corresponding to that key varies periodically with cyclic repetition at a specific rate is realized.
An electronic musical instrument in which this invention is applied is an apparatus of a system wherein successive sample point amplitude values of muscial tone waveform are stored in a memory, and addresses for reading out the musical tone waveform sample point amplitude values from this memory are designated by binary signals of a plurality of bits. Electronic muscial instruments of systems of this character have already been disclosed in the specification of U.S. Pat. No. 3,882,751.
The binary signals of a plurality of bits for reading out the waveforms from the memory are obtained by successive accumulation of a constant proportional to the frequency of the musical tone at each constant sample period. With this accumulation, the value of the binary signal increases, and the phase of the musical tone waveform read out is advanced. Accordingly, the quantity of increase of the binary signal at each sample period is constant, and the advance of the phase in a constant period (sample period) becomes constant, whereby a musical tone waveform of constant frequency is obtained.
In the case where the tonal pitch of a musical tone emitted in an electronic musical instrument of this character is to be varied rhythmically and periodically, a relatively high degree of playing technique wherein a plurality of keys must be successively depressed in a rhythmical manner has heretofore been required of the musical playing the instrument. The reason for this is that, since only a certain frequency (tonal pitch) can be obtained by merely depressing one key in a conventional instrument, appropriate keys as necessary must be selected.